1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a recording medium.
2. Description of the Related Art
Conventionally, electrophotography is generally inferior to offset printing in image stability. To bring the image stability in electrophotography close to the image stability in offset printing, various techniques have been employed. One of differences between electrophotography and offset printing is gradation expression. Electrophotography performs image processing using a line screen, a halftone dot screen, or an FM screen, for example, to express gradation. The halftone dot screen outputs an image having gradation close to gradation in offset printing compared with other screens.
Japanese Unexamined Patent Application Publication No. 2012-3180, for example, discloses a technique of using two types of screens to provide high image quality and a high degree of stability of the image quality in intermediate gradation, which are less likely to be provided by the halftone dot screen. Specifically, the technique employs two types of screens, a line screen in low-to-intermediate gradation and a void halftone dot screen (screen with dots that looks like a screen obtained by inverting a halftone dot screen) in high gradation.
The conventional technique, however, does not take into consideration a method for improving the image quality and securing the stability of the image quality in intermediate-to-high gradation where the screens are switched. As a result, the image quality and the stability may possibly deteriorate near this gradation. Furthermore, the conventional technique needs to store the two screens and perform rearrangement of dots in each dot array at an adjacent portion of the two different screens. As a result, the technique is expected to require a longer time to perform the image processing and requires a larger capacity memory than in other conventional techniques using one screen. The conventional halftone dot screen thus has a low degree of stability of the image quality in the intermediate gradation.